Wide band-cap radiation detectors operating at room temperature have been under development as an alternative for cryogenic detectors which exhibit excellent charge transport properties and unsurpassed energy resolution. Amongst these detectors, cadmium Telluride (CdTe) and cadmium Zinc Telluride (CdZnTe) are a few to have gone under extensive research and development because of their high resistivity for low leakage, high stopping power, and the ability to grow large crystals for pixilated two-dimensional (2D) array designs. However, these detectors suffer from poor charge transport properties which degrade their performance for gamma-ray spectroscopy. For example, the mobility-lifetime products for the holes in CdZnTe are typically an order of magnitude less than that of electrons. Thus, a full amplitude signal is generated only for complete charge collection due to the movement of fast electrons and slow holes, assuming negligible charge tapping.
In the case of CdZnTe, incomplete charge collection due to slow hole mobility results in depth-dependent signal variations such that the slow signal rise-time for the portion of the induced charge due to hole-movements towards cathode causes severe ballistic deficit. This phenomenon can be observed from the spectrum tailing (also called “hole tailing” for CdZnTe and “electron tailing” for a-Se) at low photon energies.
Several methods have been proposed to circumvent the problem of poor carrier mobility (e.g. poor hole mobility for CdZnTe and poor electron mobility for a-Se). They include 1) hemispherical detector structures, 2) pulse-shape discrimination and 3) charge loss correction. Hemispherical detector structures are only partially effective and their design are hard to realize for large-area pixilated two-dimensional (2D) architectures. Pulse-shape discrimination improves energy resolution but dramatically degrades detector efficiency (or sensitivity) and charge loss correction requires sophisticated readout electronics to perform proper correction and thus, dramatically limits its application in the field.
In one prior art embodiment, a radiation detector includes a grid, or contact, on its perimeter, or outer surface to assist in the charge collection process. The contact blocks charge induction from the motion of holes inside the radiation detector. However, this embodiment has only limited uses as the field that is created by the grid can not be guaranteed to be continuous which means that, for large detectors, the efficiency of the detector is reduced.
Furthermore, many current detectors are only capable of photon counting since they are limited to single pixilated operation
Therefore, there is provided a novel radiation detector which overcomes disadvantages of prior art detectors.